必要がある【ひつようがある】

必要がある means "need to", "it is necessary to": there is a need for the action. The verb before it is in the dictionary form, and ある changes for polite speech and for the past.

• × パスポートを更新して必要がある → パスポートを更新する必要がある

必要はない

"There's no need to" takes は instead of が: 必要はない, polite ひつよう必要はありません. It tells someone they can skip something, and it is common in speech as well as writing.

必要がある or なければならない

なければならない says you must, as a rule or a duty. 必要がある reports that a need exists, which suits explaining a situation or giving instructions.

With a noun

A noun for an action, such as しゅじゅつ手術 or かくにん確認, takes の before 必要がある. For a thing you need, the usual sentence is [noun] + がひつよう必要だ.